Development units, which develop electrostatic latent image formed on peripheral surface of a photoreceptor drum, are used in electrophotographic image forming apparatus. Examples of configurations of the development units are illustrated in FIG. 1A and FIG. 1B.
FIG. 1A illustrates configuration in which a development unit 52A are arranged near a photoreceptor drum 51 so as to be rotatable about a rotation axis 60. The rotation axis 60 is disposed parallel to an axis of the photoreceptor drum 51. The development unit 52A has a development roller 53, a toner regulating blade 55, and a toner feed roller 54. The development unit 52A is connected through a pressing member 57 to an inner flame 56 of an image forming apparatus. The pressing member 57 urges the development unit 52A toward the photoreceptor drum 51, thereby ensuring that peripheral surfaces of the development roller 53 and the photoreceptor drum 51 press against each other at intended force.
On the other hand, FIG. 1B illustrates configuration in which a development unit 52B are arranged so as not to rotate but to reciprocate toward or away from the photoreceptor drum 51. In this configuration, the development unit 52B is connected through a linear guide member 61 to an inner flame 62 of an image forming apparatus. The linear guide member 61 is configured to produce little friction against the development unit 52B.
As illustrated in FIG. 1A and FIG. 1B, the photoreceptor drum 51 and the development roller 53 are not fixed in relative position, and thus development nip therebetween is not likely to fluctuate even though the photoreceptor drum 51 or the development roller 53 is eccentrically disposed.
However, in electrophotographic image forming apparatus, there sometimes appears in reproduced image banding, which is streaky defect in density, due to mechanical vibration. The banding is caused by a variety of mechanical vibrations, thus there has been conducted a variety of countermeasures in accordance with cause of banding.
There is quoted, as a representative example of cause of banding, velocity fluctuation of a photoreceptor drum. For instance, when a driving gear for a photoreceptor drum is eccentrically disposed, there appears in reproduced image streaky defect in density corresponding to rotation period of the driving gear. When backlash of the driving gear is large or measure of precision of the driving gear is not satisfactory, there appears in reproduced image streaky defect in density corresponding to tooth pitch of the driving gear. Further, there may become cause of banding resonance which is caused by lack of strength of coupling for supporting a drive axis of a photoreceptor drum, or a sheet metal and a shaft for supporting a gear train.
When mechanical vibration generated in a drive system is communicated to a photoreceptor drum as disturbance, there may be employed methods of raising the precision of gears as countermeasures. When resonance occurs, there have been conducted countermeasures, such as intensity correction of structure or installation of viscoelastic member, in order to avoid or block off resonance (see Patent literature 1).
There have been also conducted countermeasures for vibration receiving side, such as applying a flywheel to a drive shaft of a photoreceptor drum in order to reduce vibration strength, adding to drive shaft of a photoreceptor drum a damper having viscous fluid body, or providing to inside of a photoreceptor drum a inertia load or dynamic damper for reducing vibration caused by rotation of a photoreceptor drum (see Patent literature 2).
Further, there exists a related art for regulating natural frequency of a development unit. In this art a vibration absorption member are applied to blade supporting member for supporting a blade.
[Patent literature 1] Japanese Patent Application Laid-Open No. H10-240067
[Patent literature 2] Japanese Patent Application Laid-Open No. H6-95562
[Patent literature 3] Japanese Patent Application Laid-Open No. H1-138580